In recent years, in a control system for an optical recording/reproducing apparatus (hereinafter, merely referred to as “optical disk apparatus”), for example with regard to loop gain control, various automatic adjustment functions or learning functions in which microcomputers are introduced have been developed. An optical disk apparatus which is provided with a loop gain adjustment function employing a microcomputer is disclosed for example in Japanese Published Patent Application No. Hei. 5-159318 or No. Hei. 5-159326. In these apparatuses, the loop gain adjustment is performed in both of a rewritable area (RW area) and a read-only memory area (ROM area) in one recording medium.
Hereinafter, a conventional optical disk apparatus will be described.
FIG. 22 is a block diagram illustrating a structure of the conventional optical disk apparatus.
In the figure, numeral 1 denotes an optical pickup, numeral 2 denotes a spindle motor, numeral 3 denotes an optical disk, numeral 4 denotes an RF amplifier, numeral 5 denotes a phase compensating circuit, numeral 6 denotes a composing circuit, numeral 7 denotes a D/A converter, numeral 8 denotes an A/D converter, numeral 9 denotes a microcomputer, numeral 10 denotes a gain adjusting circuit, numeral 11 denotes a driving circuit, and numeral 20 denotes a servo part.
The optical pickup 1 comprises a laser light source such as a laser diode; optical components such as a collimator lens, an objective lens, a polarized beam splitter and a cylindrical lens; a photo detector having a photoreceiving part of a prescribed pattern and the like, and the objective lens is driven by a biaxial actuator.
The optical pickup 1 detects a reflected light of a laser which is applied to a target track of the optical disk 3 rotated by the spindle motor 2, and sends this detection signal to the RF amplifier 4. The detection signal includes a reproduction signal for a difference in the quantity of a reflected light of a laser beam from the target track at reproduction, a focus error signal based on an astigmatism method, a tracking error signal based on a push-pull method, and address information based on a wobbling groove.
A focus servo error signal and a tracking servo error signal generated by the RF amplifier 4 are inputted via the phase compensating circuit 5 which compensates the phase of a control system to the composing circuit 6 for gain adjustment.
The microcomputer 9 outputs a disturbance signal through the D/A converter 7 to apply disturbance to the control system through the composing circuit 6. A reply signal for the applied disturbance is inputted to the microcomputer 9 through the A/D converter 8. A loop gain or a phase of the control system is calculated by arithmetic on the basis of the disturbance signal and the reply signal, and its value is outputted to the gain adjusting circuit 10 to change a resistance value in the gain adjusting circuit 10, thereby setting an optimum gain.
When the optimum gain is set, a driving signal for a focus and tracking actuator, outputted from the servo part 20 which comprises the phase compensating circuit 5, the composing circuit 6 and the gain adjusting circuit 10, is inputted to the driving circuit 11, thereby controlling the actuator.
Here, the conventional loop gain adjustment method for an optical disk on which RW areas and ROM areas are mixed will be described with reference to a flowchart shown in FIG. 23.
First, when the optical disk apparatus is started or an optical disk is mounted, the spindle motor is turned ON and the laser is turned ON (Step S101), thereby starting a spinup operation.
Next, after the focus servo is turned ON (Step S102), the tracking servo is turned ON (Step S103) and then the track hold operation is started (Step S104). First, seek to an adjustment track in the RW area is performed (Step S105), thereby performing offset adjustment and gain adjustment (Steps S106 and S108), and respective adjustment values are stored (Steps S107 and S109). Next, seek to an adjustment track in the ROM area is performed (Step S110), thereby performing offset adjustment and gain adjustment as in the RW area (Steps S111 and S113), and respective adjustment values are stored (Steps S112 and S114). These adjustment values are stored in a storage means.
When the loop gain adjustment is ended, a recording or reproducing operation is started next. When a recording or reproducing command is inputted (Step S115), a target track is retrieved (Steps S116 and S119), and it is determined whether the target track is in the RW area or the ROM area. When the target track is in the RW area, offset and gain setting for the RW area is performed (steps S117 and S118) while when the target track is in the ROM area, offset and gain setting for the ROM area is performed (Steps S120 and S121). Then, the retrieval is completed (Step S122) and then the recording or reproducing operation is started (Step S123).
The conventional loop gain adjustment method is constructed as described above, so that even when areas of various light reflectances exist on an optical disk, the loop gain can be set accurately.
However, in the prior art, there is a possibility that prerecorded areas and recorded areas are mixed in a recordable optical disk such as a CD-R as the write-once optical disk or a CD-RW as the rewritable optical disk, and when the optical pickup is moved from the prerecorded area to the recorded area or from the recorded area to the prerecorded area during the loop gain adjustment, the loop gain adjustment may not converge normally.
Further, there is a possibility that prerecorded areas and recorded areas are mixed in a RW area of a recordable optical disk such as a CD-R and a CD-RW or an optical disk on which RW areas and ROM areas are mixed, and when the optical pickup operates in this area, a prerecorded area and a recorded area have different quantities of a reflected light from the optical disk, whereby a loop gain may be varied even in the RW area of the optical disk on which the RW areas and the ROM areas are mixed. For example, when the loop gain adjustment is performed in the recorded area and the optical pickup operates in the prerecorded area, or when the loop gain adjustment is performed in the prerecorded area and the optical pickup operates in the recorded area, the loop gain is varied and the control performance is deteriorated, whereby the servo system may become unstable.
The present invention is made to solve the above-mentioned problems and has for its object to provide an optical disk apparatus which makes the loop gain adjustment converge normally even in an optical disk on which prerecorded areas and recorded areas are mixed and further has a servo system which is always stable even when a gain is significantly varied due to changes in the state of the optical disk.